Luminescent compounds with carbene ligands

ABSTRACT

An organic light emitting device is provided. The device has an anode, a cathode and an organic layer disposed between the anode and the cathode. The organic layer comprises a compound further comprising one or more carbene ligands coordinated to a metal center.

FIELD OF THE INVENTION

The present invention relates to organic light emitting devices (OLEDs),and more specifically to phosphorescent organic materials used in suchdevices. More specifically, the present invention relates tocarbene-metal complexes incorporated into OLEDs.

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a jointuniversity-corporation research agreement: Princeton University, TheUniversity of Southern California, and Universal Display Corporation.The agreement was in effect on and before the date the claimed inventionwas made, and the claimed invention was made as a result of activitiesundertaken within the scope of the agreement.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be an fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

OLED devices are generally (but not always) intended to emit lightthrough at least one of the electrodes, and one or more transparentelectrodes may be useful in an organic opto-electronic devices. Forexample, a transparent electrode material, such as indium tin oxide(ITO), may be used as the bottom electrode. A transparent top electrode,such as disclosed in U.S. Pat. Nos. 5,703,436 and 5,707,745, which areincorporated by reference in their entireties, may also be used. For adevice intended to emit light only through the bottom electrode, the topelectrode does not need to be transparent, and may be comprised of athick and reflective metal layer having a high electrical conductivity.Similarly, for a device intended to emit light only through the topelectrode, the bottom electrode may be opaque and/or reflective. Wherean electrode does not need to be transparent, using a thicker layer mayprovide better conductivity, and using a reflective electrode mayincrease the amount of light emitted through the other electrode, byreflecting light back towards the transparent electrode. Fullytransparent devices may also be fabricated, where both electrodes aretransparent. Side emitting OLEDs may also be fabricated, and one or bothelectrodes may be opaque or reflective in such devices.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. For example, for a devicehaving two electrodes, the bottom electrode is the electrode closest tothe substrate, and is generally the first electrode fabricated. Thebottom electrode has two surfaces, a bottom surface closest to thesubstrate, and a top surface further away from the substrate. Where afirst layer is described as “disposed over” a second layer, the firstlayer is disposed further away from substrate. There may be other layersbetween the first and second layer, unless it is specified that thefirst layer is “in physical contact with” the second layer. For example,a cathode may be described as “disposed over” an anode, even thoughthere are various organic layers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

The carbene ligand has been well known in organometallic chemistry, andis used to generate a wide range of thermally stable catalyticmaterials. The carbene ligands have been employed both as active groups,directly engaged in the catalytic reactions, and serving a role ofstabilizing the metal in a particular oxidation state or coordinationgeometry. However, applications of carbene ligands are not well known inphotochemistry and have yet to be used as electroluminescent compounds.

One issue with many existing organic electroluminescent compounds isthat they are not sufficiently stable for use in commercial devices. Anobject of the invention is to provide a class of organic emissivecompounds having improved stability.

In addition, prior art compounds do not include compounds that arestable emitters for high energy spectra, such as a blue spectra. Anobject of the invention is to provide a class of organic emissivecompounds that can emit light with various spectra, including highenergy spectra such as blue, in a stable manner.

SUMMARY OF THE INVENTION

An organic light emitting device is provided. The device has an anode, acathode and an organic layer disposed between the anode and the cathode.The organic layer comprises a compound further comprising one or morecarbene ligands coordinated to a metal center.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device having separate electrontransport, hole transport, and emissive layers, as well as other layers.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows the ¹H NMR spectra of mer-(F₂ppz)₂Ir(1-Ph-3-Me-imid) inCDCl₃.

FIG. 4 shows the ¹H NMR spectra of mer-(tpy)₂Ir(1-Ph-3-Me-imid) inCDCl₃.

FIG. 5 shows the ¹H NMR spectra of fac-(tpy)₂Ir(1-Ph-3-Me-imid) inCDCl₃.

FIG. 6 shows the plot of current (μA) vs. voltage (V) of amer-(tpy)₂Ir(1-Ph-3-Me-imid) device with ferrocene as an internalreference. A solvent of DMF with 0.1M Bu₄N⁺PF₆ ⁻ is used.

FIG. 7 shows the plot of current (μA) vs. voltage (V) of afac-(tpy)₂Ir(1-Ph-3-Me-imid) device with ferrocene as an internalreference. A solvent of DMF with 0.1M Bu₄N⁺PF₆ ⁻ is used.

FIG. 8 shows the absorption spectra of fac-(tpy)₂Ir(1-Ph-3-Me-imid) andmer-(tpy)₂Ir(1-Ph-3-Me-imid) in CH₂Cl₂.

FIG. 9 shows the emission spectra of mer-(tpy)₂Ir(1-Ph-3-Me-imid) in2-MeTHF at room temperature and at 77K. The compound exhibits lifetimesof 1.7 μs at room temperature and 3.3 μs at 77K.

FIG. 10 shows the emission spectra of fac-(tpy)₂Ir(1-Ph-3-Me-imid) in2-MeTHF at room temperature and at 77K. The compound exhibits lifetimesof 1.7 μs at room temperature and 3.3 μs at 77K.

FIG. 11 shows the ¹H NMR spectra of [(1-Ph-3-Me-imid)₂IrCl]₂ in CDCl₃.

FIG. 12 shows the ¹H NMR spectra of (1-Ph-3-Me-imid)₂Ir(t-Bu-bpy)⁺ inCDCl₃.

FIG. 13 shows the absorption spectra of (1-Ph-3-Me-imid)₂Ir(t-Bu-bpy)⁺in CH₂Cl₂.

FIG. 14 shows the emission spectra of (1-Ph-3-Me-imid)₂Ir(t-Bu-bpy)⁺ in2-MeTHF at 77K and (1-Ph-3-Me-imid)₂Ir(t-Bu-bpy)⁺ in CH₂Cl₂ at roomtemperature. The compound exhibits lifetimes of 0.70 μs at roomtemperature and 6.0 μs at 77K.

FIG. 15 shows the ¹H NMR spectra of mer-Ir(1-Ph-3-Me-imid)₃ in CDCl₃.

FIG. 16 shows the ¹³C NMR spectra of mer-Ir(1-Ph-3-Me-imid)₃ in CDCl₃.

FIG. 17 shows the plot of current (μA) vs. voltage (V) of amer-Ir(1-Ph-3-Me-imid)₃ device with ferrocene as an internal reference.A solvent of DMF with 0.1M Bu₄N⁺PF₆ ⁻ is used.

FIG. 18 shows the emission spectra of mer-Ir(1-Ph-3-Me-imid)₃ in 2-MeTHFat room temperature and at 77K.

FIG. 19 shows the ¹H NMR spectra of fac-Ir(1-Ph-3-Me-imid)₃ in CDCl₃.

FIG. 20 shows the absorption spectra of fac-Ir(1-Ph-3-Me-imid)₃ inCH₂Cl₂.

FIG. 21 shows the emission spectra of fac-Ir(1-Ph-3-Me-imid)₃ in 2-MeTHFat room temperature and at 77K. The device exhibits lifetimes of 0.50 μsat room temperature and 6.8 μs at 77K.

FIG. 22 shows the ¹H NMR spectra of 1-Ph-3-Me-benzimid in CDCl₃.

FIG. 23 shows the ¹H NMR spectra of fac-Ir(1-Ph-3-Me-benzimid)₃ inCDCl₃.

FIG. 24 shows the plot of current (mA) vs. voltage (V) of afac-Ir(1-Ph-3-Me-benzimid)₃ device with ferrocene as an internalreference. A solvent of anhydrous DMF is used.

FIG. 25 shows the emission spectra of fac-Ir(1-Ph-3-Me-benzimid)₃ in2-MeTHF at room temperature and at 77K. The device emits a spectrum atCIE 0.17, 0.04.

FIG. 26 shows the emission spectra of (Ir-Fl-Me-imidazolate)₃ in 2-MeTHFat roomo temperature and at 77K. The device exhibits lifetimes of 5 μsat room temperature and 35 μs at 77K.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence may be referred to asa “forbidden” transition because the transition requires a change inspin states, and quantum mechanics indicates that such a transition isnot favored. As a result, phosphorescence generally occurs in a timeframe exceeding at least 10 nanoseconds, and typically greater than 100nanoseconds. If the natural radiative lifetime of phosphorescence is toolong, triplets may decay by a non-radiative mechanism, such that nolight is emitted. Organic phosphorescence is also often observed inmolecules containing heteroatoms with unshared pairs of electrons atvery low temperatures. 2,2′-bipyridine is such a molecule. Non-radiativedecay mechanisms are typically temperature dependent, such that amaterial that exhibits phosphorescence at liquid nitrogen temperaturesmay not exhibit phosphorescence at room temperature. But, asdemonstrated by Baldo, this problem may be addressed by selectingphosphorescent compounds that do phosphoresce at room temperature.Representative emissive layers include doped or un-doped phosphorescentorgano-metallic materials such as disclosed in U.S. Pat. Nos. 6,303,238and 6,310,360; U.S. Patent Application Publication Nos. 2002-0034656;2002-0182441; amd 2003-0072964; and WO-02/074015.

Generally, the excitons in an OLED are believed to be created in a ratioof about 3:1, i.e., approximately 75% triplets and 25% singlets. See,Adachi et al., “Nearly 100% Internal Phosphorescent Efficiency In AnOrganic Light Emitting Device,” J. Appl. Phys., 90, 5048 (2001), whichis incorporated by reference in its entirety. In many cases, singletexcitons may readily transfer their energy to triplet excited states via“intersystem crossing,” whereas triplet excitons may not readilytransfer their energy to singlet excited states. As a result, 100%internal quantum efficiency is theoretically possible withphosphorescent OLEDs. In a fluorescent device, the energy of tripletexcitons is generally lost to radiationless decay processes that heat-upthe device, resulting in much lower internal quantum efficiencies. OLEDsutilizing phosphorescent materials that emit from triplet excited statesare disclosed, for example, in U.S. Pat. No. 6,303,238, which isincorporated by reference in its entirety.

Phosphorescence may be preceded by a transition from a triplet excitedstate to an intermediate non-triplet state from which the emissive decayoccurs. For example, organic molecules coordinated to lanthanideelements often phosphoresce from excited states localized on thelanthanide metal. However, such materials do not phosphoresce directlyfrom a triplet excited state but instead emit from an atomic excitedstate centered on the lanthanide metal ion. The europium diketonatecomplexes illustrate one group of these types of species.

Phosphorescence from triplets can be enhanced over fluorescence byconfining, preferably through bonding, the organic molecule in closeproximity to an atom of high atomic number. This phenomenon, called theheavy atom effect, is created by a mechanism known as spin-orbitcoupling. Such a phosphorescent transition may be observed from anexcited metal-to-ligand charge transfer (MLCT) state of anorganometallic molecule such as tris(2-phenylpyridine)iridium(III).

As used herein, the term “triplet energy” refers to an energycorresponding to the highest energy feature discernable in thephosphorescence spectrum of a given material. The highest energy featureis not necessarily the peak having the greatest intensity in thephosphorescence spectrum, and could, for example, be a local maximum ofa clear shoulder on the high energy side of such a peak.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, and a cathode 160. Cathode 160 is acompound cathode having a first conductive layer 162 and a secondconductive layer 164. Device 100 may be fabricated by depositing thelayers described, in order.

Substrate 110 may be any suitable substrate that provides desiredstructural properties. Substrate 110 may be flexible or rigid. Substrate110 may be transparent, translucent or opaque. Plastic and glass areexamples of preferred rigid substrate materials. Plastic and metal foilsare examples of preferred flexible substrate materials. Substrate 110may be a semiconductor material in order to facilitate the fabricationof circuitry. For example, substrate 110 may be a silicon wafer uponwhich circuits are fabricated, capable of controlling OLEDs subsequentlydeposited on the substrate. Other substrates may be used. The materialand thickness of substrate 110 may be chosen to obtain desiredstructural and optical properties.

Anode 115 may be any suitable anode that is sufficiently conductive totransport holes to the organic layers. The material of anode 115preferably has a work function higher than about 4 eV (a “high workfunction material”). Preferred anode materials include conductive metaloxides, such as indium tin oxide (ITO) and indium zinc oxide (IZO),aluminum zinc oxide (AlZnO), and metals. Anode 115 (and substrate 110)may be sufficiently transparent to create a bottom-emitting device. Apreferred transparent substrate and anode combination is commerciallyavailable ITO (anode) deposited on glass or plastic (substrate). Aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. Nos. 5,844,363 and 6,602,540 B2, which are incorporated byreference in their entirety. Anode 115 may be opaque and/or reflective.A reflective anode 115 may be preferred for some top-emitting devices,to increase the amount of light emitted from the top of the device. Thematerial and thickness of anode 115 may be chosen to obtain desiredconductive and optical properties. Where anode 115 is transparent, theremay be a range of thickness for a particular material that is thickenough to provide the desired conductivity, yet thin enough to providethe desired degree of transparency. Other anode materials and structuresmay be used.

Hole transport layer 125 may include a material capable of transportingholes. Hole transport layer 130 may be intrinsic (undoped), or doped.Doping may be used to enhance conductivity. a-NPD and TPD are examplesof intrinsic hole transport layers. An example of a p-doped holetransport layer is m-MTDATA doped with F₄-TCNQ at a molar ratio of 50:1,as disclosed in U.S. Patent Application Publication No. 2002-0071963 A1to Forrest et al., which is incorporated by reference in its entirety.Other hole transport layers may be used.

Emissive layer 135 may include an organic material capable of emittinglight when a current is passed between anode 115 and cathode 160.Preferably, emissive layer 135 contains a phosphorescent emissivematerial, although fluorescent emissive materials may also be used.Phosphorescent materials are preferred because of the higher luminescentefficiencies associated with such materials. Emissive layer 135 may alsocomprise a host material capable of transporting electrons and/or holes,doped with an emissive material that may trap electrons, holes, and/orexcitons, such that excitons relax from the emissive material via aphotoemissive mechanism. Emissive layer 135 may comprise a singlematerial that combines transport and emissive properties. Whether theemissive material is a dopant or a major constituent, emissive layer 135may comprise other materials, such as dopants that tune the emission ofthe emissive material. Emissive layer 135 may include a plurality ofemissive materials capable of, in combination, emitting a desiredspectrum of light. Examples of phosphorescent emissive materials includeIr(ppy)₃. Examples of fluorescent emissive materials include DCM andDMQA. Examples of host materials include Alq₃, CBP and mCP. Examples ofemissive and host materials are disclosed in U.S. Pat. No. 6,303,238 toThompson et al., which is incorporated by reference in its entirety.Emissive material may be included in emissive layer 135 in a number ofways. For example, an emissive small molecule may be incorporated into apolymer. This may be accomplished by several ways: by doping the smallmolecule into the polymer either as a separate and distinct molecularspecies; or by incorporating the small molecule into the backbone of thepolymer, so as to form a co-polymer; or by bonding the small molecule asa pendant group on the polymer. Other emissive layer materials andstructures may be used. For example, a small molecule emissive materialmay be present as the core of a dendrimer.

Electron transport layer 140 may include a material capable oftransporting electrons. Electron transport layer 140 may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity. Alq₃ isan example of an intrinsic electron transport layer. An example of ann-doped electron transport layer is BPhen doped with Li at a molar ratioof 1:1, as disclosed in U.S. Patent Application Publication No.2002-0071963 A1 to Forrest et al., which is incorporated by reference inits entirety. Other electron transport layers may be used.

The charge carrying component of the electron transport layer may beselected such that electrons can be efficiently injected from thecathode into the LUMO (Lowest Unoccupied Molecular Orbital) level of theelectron transport layer. The “charge carrying component” is thematerial responsible for the LUMO that actually transports electrons.This component may be the base material, or it may be a dopant. The LUMOlevel of an organic material may be generally characterized by theelectron affinity of that material and the relative electron injectionefficiency of a cathode may be generally characterized in terms of thework function of the cathode material. This means that the preferredproperties of an electron transport layer and the adjacent cathode maybe specified in terms of the electron affinity of the charge carryingcomponent of the ETL and the work function of the cathode material. Inparticular, so as to achieve high electron injection efficiency, thework function of the cathode material is preferably not greater than theelectron affinity of the charge carrying component of the electrontransport layer by more than about 0.75 eV, more preferably, by not morethan about 0.5 eV. Similar considerations apply to any layer into whichelectrons are being injected.

Cathode 160 may be any suitable material or combination of materialsknown to the art, such that cathode 160 is capable of conductingelectrons and injecting them into the organic layers of device 100.Cathode 160 may be transparent or opaque, and may be reflective. Metalsand metal oxides are examples of suitable cathode materials. Cathode 160may be a single layer, or may have a compound structure. FIG. 1 shows acompound cathode 160 having a thin metal layer 162 and a thickerconductive metal oxide layer 164. In a compound cathode, preferredmaterials for the thicker layer 164 include ITO, IZO, and othermaterials known to the art. U.S. Pat. Nos. 5,703,436, 5,707,745,6,548,956 B2, and 6,576,134 B2, which are incorporated by reference intheir entireties, disclose examples of cathodes including compoundcathodes having a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thepart of cathode 160 that is in contact with the underlying organiclayer, whether it is a single layer cathode 160, the thin metal layer162 of a compound cathode, or some other part, is preferably made of amaterial having a work function lower than about 4 eV (a “low workfunction material”). Other cathode materials and structures may be used.

Blocking layers may be used to reduce the number of charge carriers(electrons or holes) and/or excitons that leave the emissive layer. Anelectron blocking layer 130 may be disposed between emissive layer 135and the hole transport layer 125, to block electrons from leavingemissive layer 135 in the direction of hole transport layer 125.Similarly, a hole blocking layer 140 may be disposed between emissivelayer 135 and electron transport layer 145, to block holes from leavingemissive layer 135 in the direction of electron transport layer 140.Blocking layers may also be used to block excitons from diffusing out ofthe emissive layer. The theory and use of blocking layers is describedin more detail in U.S. Pat. No. 6,097,147 and U.S. Patent ApplicationPublication No. 2002-0071963 A1 to Forrest et al., which areincorporated by reference in their entireties.

As used herein, the term “blocking layer” means that the layer providesa barrier that significantly inhibits transport of charge carriersand/or excitons through the device, without suggesting that the layernecessarily completely blocks the charge carriers and/or excitons. Thepresence of such a blocking layer in a device may result insubstantially higher efficiencies as compared to a similar devicelacking a blocking layer. Also, a blocking layer may be used to confineemission to a desired region of an OLED.

Generally, injection layers are comprised of a material that may improvethe injection of charge carriers from one layer, such as an electrode oran organic layer, into an adjacent organic layer. Injection layers mayalso perform a charge transport function. In device 100, hole injectionlayer 120 may be any layer that improves the injection of holes fromanode 115 into hole transport layer 125. CuPc is an example of amaterial that may be used as a hole injection layer from an ITO anode115, and other anodes. In device 100, electron injection layer 150 maybe any layer that improves the injection of electrons into electrontransport layer 145. LiF/Al is an example of a material that may be usedas an electron injection layer into an electron transport layer from anadjacent layer. Other materials or combinations of materials may be usedfor injection layers. Depending upon the configuration of a particulardevice, injection layers may be disposed at locations different thanthose shown in device 100. More examples of injection layers areprovided in U.S. patent application Ser. No. 09/931,948 to Lu et al.,which is incorporated by reference in its entirety. A hole injectionlayer may comprise a solution deposited material, such as a spin-coatedpolymer, e.g., PEDOT:PSS, or it may be a vapor deposited small moleculematerial, e.g., CuPc or MTDATA.

A hole injection layer (HIL) may planarize or wet the anode surface soas to provide efficient hole injection from the anode into the holeinjecting material. A hole injection layer may also have a chargecarrying component having HOMO (Highest Occupied Molecular Orbital)energy levels that favorably match up, as defined by theirherein-described relative ionization potential (IP) energies, with theadjacent anode layer on one side of the HIL and the hole transportinglayer on the opposite side of the HIL. The “charge carrying component”is the material responsible for the HOMO that actually transports holes.This component may be the base material of the HIL, or it may be adopant. Using a doped HIL allows the dopant to be selected for itselectrical properties, and the host to be selected for morphologicalproperties such as wetting, flexibility, toughness, etc. Preferredproperties for the HIL material are such that holes can be efficientlyinjected from the anode into the HIL material. In particular, the chargecarrying component of the HIL preferably has an IP not more than about0.7 eV greater that the IP of the anode material. More preferably, thecharge carrying component has an IP not more than about 0.5 eV greaterthan the anode material. Similar considerations apply to any layer intowhich holes are being injected. HIL materials are further distinguishedfrom conventional hole transporting materials that are typically used inthe hole transporting layer of an OLED in that such HIL materials mayhave a hole conductivity that is substantially less than the holeconductivity of conventional hole transporting materials. The thicknessof the HIL of the present invention may be thick enough to helpplanarize or wet the surface of the anode layer. For example, an HILthickness of as little as 10 nm may be acceptable for a very smoothanode surface. However, since anode surfaces tend to be very rough, athickness for the HIL of up to 50 nm may be desired in some cases.

A protective layer may be used to protect underlying layers duringsubsequent fabrication processes. For example, the processes used tofabricate metal or metal oxide top electrodes may damage organic layers,and a protective layer may be used to reduce or eliminate such damage.In device 100, protective layer 155 may reduce damage to underlyingorganic layers during the fabrication of cathode 160. Preferably, aprotective layer has a high carrier mobility for the type of carrierthat it transports (electrons in device 100), such that it does notsignificantly increase the operating voltage of device 100. CuPc, BCP,and various metal phthalocyanines are examples of materials that may beused in protective layers. Other materials or combinations of materialsmay be used. The thickness of protective layer 155 is preferably thickenough that there is little or no damage to underlying layers due tofabrication processes that occur after organic protective layer 160 isdeposited, yet not so thick as to significantly increase the operatingvoltage of device 100. Protective layer 155 may be doped to increase itsconductivity. For example, a CuPc or BCP protective layer 160 may bedoped with Li. A more detailed description of protective layers may befound in U.S. patent application Ser. No. 09/931,948 to Lu et al., whichis incorporated by reference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,an cathode 215, an emissive layer 220, a hole transport layer 225, andan anode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190, Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, which is incorporated byreference in its entirety. Other suitable deposition methods includespin coating and other solution based processes. Solution basedprocesses are preferably carried out in nitrogen or an inert atmosphere.For the other layers, preferred methods include thermal evaporation.Preferred patterning methods include deposition through a mask, coldwelding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819,which are incorporated by reference in their entireties, and patterningassociated with some of the deposition methods such as ink-jet and OVJD.Other methods may also be used. The materials to be deposited may bemodified to make them compatible with a particular deposition method.For example, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix. Many of the devices are intended for use in a temperaturerange comfortable to humans, such as 18 degrees C. to 30 degrees C., andmore preferably at room temperature (20-25 degrees C.).

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

A compound comprising a carbene ligand bound to a metal center isprovided. Carbene compounds include small molecules, dendrimers, andpolymers that include a carbene-metal bond. In one embodiment, thecompound is a phosphorescent emissive material, preferably a dopant. Thecompound may also be doped into a wide band gap host material such asdisclosed in U.S. patent application Ser. No. 10/680,066, which isincorporated by reference in its entirety, or it may be doped into aninert wide band gap host such as disclosed in WO-074015, which isincorporated by reference in its entirety.

In another embodiment, the metal-carbene compound is a host material inan emissive layer. For example, the metal-carbene compound may be usedas a high energy host materials for doped blue devices. The dopant inthis case could be a triplet emitter or a singlet emitter (usingphosphor sensitized fluorescence). Additionally, the high band gap ofmetal-carbene compounds may make these materials effective in carrierblocking and transporting layers. It is believed that metal-carbenecompounds described herein have improved thermal stability whenincorporated into an organic light emitting device due to thecarbene-metal bond, as compared to prior art compounds without acarbene-metal bond.

As used herein, the term “carbene” refers to compounds having a divalentcarbon atom with only six electrons in its valence shell when notcoordinated to a metal. A useful exercise to determine whether a ligandincludes a carbene-metal bond is to mentally deconstruct the complex asa metal fragment and a ligand, and to then determine whether a carbonatom in the ligand that was previously bound to the metal is a neutraldivalent carbon atom in the deconstructed state. The resonance forms ofa preferred embodiment may be shown as:

This definition of carbene is not limited to metal-carbene complexessynthesized from carbenes, but is rather intended to address the orbitalstructure and electron distribution associated with the carbon atom thatis bound to the metal. The definition recognizes that the “carbene” maynot technically be divalent when bound to the metal, but it would bedivalent if it were detached from the metal. Although many suchcompounds are synthesized by first synthesizing a carbene and thenbinding it to a metal, the definition is intended to encompass compoundssynthesized by other methods that have a similar orbital structure andelectron configuration. Lowry & Richardson, Mechanism and Theory inOrganic Chemistry 256 (Harper & Row, 1976) defines “carbene” in a waythat is consistent with the way the term is used herein. Some referencesmay define “carbene” as a carbon ligand that forms a double bond to ametal. While this definition is not being used in the presentapplication, there may be some overlap between the two definitions.

The term “organometallic” as used herein is as generally understood byone of ordinary skill in the art and as given, for example, in“Inorganic Chemistry” (2nd Edition) by Gary L. Miessler and Donald A.Tarr, Pentice-Hall (1998). Thus, the term organometallic refers tocompounds which have an organic group bonded to a metal through acarbon-metal bond. This class does not include per se coordinationcompounds, which are substances having only donor bonds fromheteroatoms, such as metal complexes of anines, halides, pseudohalides(CN, etc.), and the like. In practice organometallic compounds generallycomprise, in addition to one or more carbon-metal bonds to an organicspecies, one or more donor bonds from a heteroatom. The carbon-metalbond to an organic species refers to a direct bond between a metal and acarbon atom of an organic group, such as phenyl, alkyl, alkenyl, etc.,but does not refer to a metal bond to an “inorganic carbon,” such as thecarbon of CN.

Carbene ligands are especially desirable in OLED applications due to thehigh thermal stability exhibited by metal-carbene complexes. It isbelieved that the carbene, which behaves much as an electron donativegroup, generally bonds strongly to the metals, thus forming a morethermally stable complex than, for example, previous cyclometallatedcomplexes used as phosphorescent emitters. It is also believed thatcarbene analogs of ligands employed in prior phosphorescent emissivematerials (for example the phenylpyridine or Irppy, etc.) may exhibitgreater stability and emit at substantially higher energy than theirprior art analogs.

As used herein, a “non-carbene analog” of a metal carbene compoundrefers to ligands in the prior art having a substantially similarchemical structure to the metal-carbene compound, but unlike the carbenecompounds of the present invention, which features a carbene-metal bond,the analog has some other bond, such as a carbon-metal or anitrogen-metal bond, in place of the carbene-metal bond. For example,Ir(ppz)₃ has a nitrogen in each ligand bound to the Ir.Ir(1-phenylimidazolin-2-ylidene) is analogous to Ir(ppz)₃ where thenitrogen bound to the Ir has been replaced with a carbene bound to theIr, and where the atoms surrounding the carbene have been changed tomake the carbon a carbene. Thus, embodiments of the present inventioninclude metal-carbene complexes (e.g. Ir(1-phenylimidazolin-2-ylidene)with similar structures to prior art emissive compounds (e.g. Ir(ppz)₃).

Examples of prior art emissive compounds include Ir(ppy)₃ and Ir(ppz)₃,discussed above. Other examples are disclosed in the references below,which are incorporated herein by reference in their entirety. Inpreferred embodiments, the carbene ligands are imidazoles, pyrazoles,benzimidazoles, and pyrroles.

It is believed that the carbene-metal bond in Ir(1-Ph-3-Me-imid)₃ isstronger than the N-metal bond in Irppz. Moreover, due to the nature ofa carbene-metal bond, it is believed that replacing a carbon-metal bondor nitrogen-metal bond in existing emissive organometallic moleculeswith a carbene-metal bond (making other changes as needed to make thecarbon atom a carbene) may result in an emissive molecule that is morestable than the non-carbene analog, and that has stronger spin-orbitcoupling. It is further believed that the emissive spectra of themolecule including a carbene may be different from the emissive spectraof the analog without a carbene.

Metal-carbene complexes may be tuned to emit a wide variety of spectrafrom the near-ultraviolet across the entire visible spectra by theselection of substituents and/or chemical groups on the ligand(s). Moresignificantly, it may now be possible to obtain saturated blue coloremissions with peak wavelengths at about 450 nm. Because it is believedto be materially easier to reduce than to increase the triplet energy bytuning an emissive compound, the ability to make stable blue emitters atsuch high energies would also allow for the possibility of obtaining anycolor by reducing the energy so as to red-shift the emission. Forexample, FIG. 18 shows that Ir(1-Ph-3-Me-imid)₃, which is a preferredembodiment of this invention, in a 2-MeTHF solution emits in the near-UVspectra at a wavelength of about 380 nm at 77 K and at room temperature.The substitution of a fluorenyl group for the phenyl group attached tothe methylimidazole results in a red-shift in the emission as shown inFIG. 26. Thus, FIG. 26 shows Ir-(FlMeImidazole)₃, which is anotherembodiment of this invention, to emit at the visible part of the spectraat a wavelength of 462 nm at 77 K and at 466 nm at room temperature.

The appropriate selection of substituents and/or chemical groupsattached to carbene ligands may also minimize quantum efficiency lossesassociated with increasing temperatures. The observable difference inlifetime measurements between emission at room temperature and at lowtemperatures (e.g. 77 K) is believed to be attributed to non-radiativequenching mechanisms that compete with phosphorescent emission. Suchquenching mechanisms are further believed to be thermally activated, andconsequently, at cooler temperatures of about 77 K, where energy lossdue to quenching is not an issue, quantum efficiency is about 100%. Forexample, FIG. 21 shows the emission spectra of fac-Ir(1-Ph-3-Me-imid)₃in 2-MeTHF. The compound exhibits a lifetime of 6.8 μs at 77 K and 0.50μs at room temperature, and the difference may be attributed toquenching mechanisms. It is believed that appropriate substituents onthe carbene ligand may increase quantum efficiency at room temperatureand correspondingly show longer lifetimes.

Due to the nature of the carbene-metal bond, the emission of a carbeneanalog may be substantially different from that of its non-carbeneanalog, and the emission of the carbene analog may be stable and at ahigher energy than previously obtainable with stable non-carbenecompounds. Embodiments of the present invention shown in FIGS. 18, 21,25, and 26, show higher energy emissions than have previously beenobtained with other phosphorescent organometallic emissive materials.

The strong metal-carbon bond is also believed to lead to greaterspin-orbit coupling in metal carbene complexes. Moreover, the tripletenergy of coordinated carbenes are shown to be significantly higher thanpyridine analogs. FIG. 18 shows the emission spectra ofmer-Ir(1-Ph-3-Me-imid)₃, which is one of the embodiments of theinvention. The emission is shown to be in the near-ultraviolet range ofthe spectrum even at room temperature. It is believed herein that othermetal carbene complexes may be capable of emitting at similarly highenergies due to the strong metal-ligand bond associated with carbeneligands.

The stability of metal-carbene complexes may also allow increasedversatility in the types of ligands and metals that may be used asphosphorescent emitters in OLEDs. The strong metal carbene bond mayallow a variety of metals to form useful phosphorescent complexes withcarbene ligands to give novel emissive compounds. For example, oneembodiment includes gold bonded to a carbene ligand. Additionally,although cyclometallated complexes are preferred embodiments, thepresent invention is not limited to such embodiments. The increasedstrength of a metal-carbene bond, as compared to other types of bondswith metal, may make monodentate ligands feasible for use as emissivematerials. Until recently, bidentate ligands were strongly preferred dueto stability concerns. Thus, embodiments include monodentate carbeneligands as well as bidentate. Embodiments also include tridentatecarbene ligands, which may be quite stable, and many examples are foundin the art, such as those disclosed in Koizumi et al., Organometallics2003, 22, 970-975. Other embodiments may also feature a tetradentateligand, such as porphyrin analogs in which one or more nitrogens arereplaced by a carbene, which is disclosed in Bourissou et al. Chem Rev.2000, 100, 39-91. Still other embodiments may include metallaquinonecarbenes, which are compounds in which one of the oxygen atoms of aquinone has been replaced by a metal, such as those disclosed inAshekenazi et al., J. Am. Chem. Soc. 2000, 122, 8797-8798. In addition,The metal-carbene compound may be present as part of a multi-dentategroup such as disclosed in U.S. patent application Ser. No. 10/771,423to Ma et al., which is incorporated by reference in its entirety.

It is believed that many of the (C,C) or (C,N) ligands of many existingelectroluminescent compounds may be modified to create an analogous(C,C) ligand including a carbene. Specific non limiting examples of suchmodification include:

-   -   (1) the substituents on the carbene-bonded branch of the        (C,C)-ligand and the substituents on the        mono-anionic-carbon-bonded branch of the (C,C)-ligand may be        independently selected from the group consisting of        -   (a) the substituents on the N-bonded branch of the prior art            (C,N)-ligands, such as disclosed in the references listed            below, which is typically but not necessarily a pyridine            group; and        -   (b) the substituents on the mono-anionic-carbon-bonded            branch of the prior art (C,N)-ligands, such as disclosed in            the references listed below, which is typically but not            necessarily a phenyl group;        -   (c) and/or a combination thereof; and    -   (2) the compounds including the metal-carbene bonds may further        include ancillary ligands selected from the group consisting of        the ancillary ligands such as disclosed in the following        references:        U.S. Pat. Application Publ. No. 2002-0034656 (K&K 10020/15303),        FIGS. 11-50, U.S. Pat. Application Publ. No. 2003-0072964        (Thompson et al.), paragraphs 7-132; and FIGS. 1-8; U.S. Pat.        Application Publ. No. 2002-0182441 (Lamansky et al.), paragraphs        13-165, including FIGS. 1-9(g); U.S. Pat. No. 6,420,057 B1 (Ueda        et al.), col. 1, line 57, through col. 88, line 17, including        each compound I-1 through XXIV-12; U.S. Pat. No. 6,383,666 B1        (Kim et al.), col. 2, line 9, through col. 21, line 67; U.S.        Pat. Application Publ. No. 2001-0015432 A1 (Igarashi et al.),        paragraphs 2-57, including compounds (1-1) through (1-30); U.S.        Pat. Application Publ. No. 2001-0019782 A1 (Igarashi et al.),        paragraphs 13- 126, including compounds (1-1) through (1-70),        and (2-1) through (2-20); U.S. Pat. Application Publ. No.        2002-0024293 (Igarashi et al.), paragraphs 7-95, including        general formulas K-I through K-VI, and example compounds (K-1)        through (K-25); U.S. Pat. Application Publ. No. 2002-0048689 A1        (Igarashi et al.), paragraphs 5-134, including compounds 1-81,        and example compounds (1-1) through (1-81); U.S. Pat.        Application Publ. No. 2002-0063516 (Tsuboyama et al.),        paragraphs 31-161, including each compound 1-16; U.S. Pat.        Application Publ. No. 2003-0068536 (Tsuboyama et al.),        paragraphs 31-168, including each compound in Tables 1-17,        corresponds to EP-1-239-526-A2; U.S. Pat. Application Publ. No.        2003-0091862 (Tokito et al.), paragraphs 10-190, including each        compound in Tables 1-17, corresponds to EP-1-239-526-A2; U.S.        Pat. Application Publ. No. 2003-0096138 (Lecloux et al.),        paragraphs 8-124, including FIGS. 1-5; U.S. Pat. Application        Publ. No. 2002-0190250 (Grushin et al.), paragraphs 9-191; U.S.        Pat. Application Publ. No. 2002-0121638 (Grushin et al.),        paragraphs 8-125; U.S. Pat. Application Publ. No. 2003-0068526        (Kamatani et al.), paragraphs 33-572, including each compound in        Tables 1-23; U.S. Pat. Application Publ. No. 2003-0141809        (Furugori et al.), paragraphs 29-207; U.S. Pat. Application        Publ. No. 2003-0162299 A1 (Hsieh et al.), paragraphs 8-42; WO        03/084972, (Stossel et al.), Examples 1-33; WO 02/02714 A2        (Petrov et al.), pages 2-30, including each compound in Tables        1-5; EP 1-191-613 A1 (Takiguchi et al.), paragraphs 26-87,        including each compound in Tables 1-8, (corresponding to U.S.        Pat. Application Publ. No. 2002-0064681); and EP 1-191-614 A2        (Tsuboyama et al.), paragraphs 25-86, including each compound in        Tables 1-7; which are incorporated herein by reference in their        entirety.

Carbene ligands may be synthesized using methods known in the art, suchas those disclosed in Cattoën, et al., J. Am. Chem. Soc., 2004, 126;1342-1343; Chiu-Yuen Wong, et al, Organometallics 2004, 23, 2263-2272;Klapars, et al, J. Am. Chem. Soc., 2001, 123; 7727-7729; Bourissou etal. Chem Rev. 2000, 100, 39-91; Siu-Wai Lai, et al, Organometallics1999, 18, 3327-3336; Wen-Mei Xue et al., Organometallics 1998, 17,1622-1630; Wang & Lin, Organometallics 1998, 17, 972-975; Cardin, etal., Chem Rev. 1972, 5, 545-574; and other references discussed herein.

In one embodiment, a phosphorescent emissive compound having thefollowing formula is provided:

wherein Z¹ and Z² may be a carbon containing moiety, an amine containingmoiety, oxygen containing moiety, a phosphine containing moiety, and asulfur containing moiety.

In another embodiment, the compound has the structure:

in which the ligands have the structure:

in which

-   M is a metal;-   the dotted lines represent optional double bonds;-   each Z₁, A, and A′ is independently selected from C, N, O, P, or S;    R₁, R₂, and R₃ are independently selected from H, alkyl, aryl or    heteroaryl; and additionally or alternatively, one or more of R₁ and    R₂ and R₂ and R₃ together form independently a 5 or 6-member cyclic    group, wherein said cyclic group is cycloalkyl, cycloheteroalkyl,    aryl or heteroaryl; and wherein said cyclic group is optionally    substituted by one or more substituents J; each substituent J is    independently selected from the group consisting of R′, O—R′,    N(R′)₂, SR′, C(O)R′, C(O)OR′, C(O)NR′₂, CN, NO₂, SO₂, SOR′, or    SO₃R′, and additionally, or alternatively, two J groups on adjacent    ring atoms form a fused 5- or 6-membered aromatic group; each R′ is    independently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl,    aralkyl, aryl, and heteroaryl;-   (X—Y) is selected from a photoactive ligand or an ancillary ligand,-   a is 0, 1, or 2.-   m is a value from 1 to the maximum number of ligands that may be    attached to the metal;-   m+n is the maximum number of ligands that may be attached to metal    M.

The term “halo” or “halogen” as used herein includes fluorine, chlorine,bromine and iodine.

The term “alkyl” as used herein contemplates both straight and branchedchain alkyl radicals. Preferred alkyl groups are those containing fromone to fifteen carbon atoms and includes methyl, ethyl, propyl,isopropyl, butyl, isobutyl, tert-butyl, and the like. Additionally, thealkyl group may be optionally substituted with one or more substituentsselected from halo, CN, CO₂R, C(O)R, NR₂, cyclic-amino, NO₂, and OR.

The term “cycloalkyl” as used herein contemplates cyclic alkyl radicals.Preferred cycloalkyl groups are those containing 3 to 7 carbon atoms andincludes cyclopropyl, cyclopentyl, cyclohexyl, and the like.Additionally, the cycloalkyl group may be optionally substituted withone or more substituents selected from halo, CN, CO₂R, C(O)R, NR₂,cyclic-amino, NO₂, and OR.

The term “alkenyl” as used herein contemplates both straight andbranched chain alkene radicals. Preferred alkenyl groups are thosecontaining two to fifteen carbon atoms. Additionally, the alkenyl groupmay be optionally substituted with one or more substituents selectedfrom halo, CN, CO₂R, C(O)R, NR₂, cyclic-amino, NO₂, and OR.

The term “alkynyl” as used herein contemplates both straight andbranched chain alkyne radicals. Preferred alkyl groups are thosecontaining two to fifteen carbon atoms. Additionally, the alkynyl groupmay be optionally substituted with one or more substituents selectedfrom halo, CN, CO₂R, C(O)R, NR₂, cyclic-amino, NO₂, and OR.

The terms “alkylaryl” as used herein contemplates an alkyl group thathas as a substituent an aromatic group. Additionally, the alkylarylgroup may be optionally substituted on the aryl with one or moresubstituents selected from halo, CN, CO₂R, C(O)R, NR₂, cyclic-amino,NO₂, and OR.

The term “heterocyclic group” as used herein contemplates non-aromaticcyclic radicals. Preferred heterocyclic groups are those containing 3 or7 ring atoms which includes at least one hetero atom, and includescyclic amines such as morpholino, piperdino, pyrrolidino, and the like,and cyclic ethers, such as tetrahydrofuran, tetrahydropyran, and thelike.

The term “aryl” or “aromatic group” as used herein contemplatessingle-ring groups and polycyclic ring systems. The polycyclic rings mayhave two or more rings in which two carbons are common by two adjoiningrings (the rings are “fused”) wherein at least one of the rings isaromatic, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl,heterocycles and/or heteroaryls.

The term “heteroaryl” as used herein contemplates single-ringhetero-aromatic groups that may include from one to three heteroatoms,for example, pyrrole, furan, thiophene, imidazole, oxazole, thiazole,triazole, pyrazole, pyridine, pyrazine and pyrimidine, and the like. Theterm heteroaryl also includes polycyclic hetero-aromatic systems havingtwo or more rings in which two atoms are common to two adjoining rings(the rings are “fused”) wherein at least one of the rings is aheteroaryl, e.g., the other rings can be cycloalkyls, cycloalkenyls,aryl, heterocycles and/or heteroaryls.

All value ranges, for example those given for n and m, are inclusiveover the entire range. Thus, for example, a range between 0-4 wouldinclude the values 0, 1, 2, 3 and 4.

Embodiments include photoactive carbene ligands. A ligand is referred toas “photoactive” because it is believed that it contributes to thephotoactive properties of the emissive material. m represents the numberof photoactive ligands. For example, for Ir, m may be 1, 2 or 3. n, thenumber of “ancillary” ligands of a particular type, may be any integerfrom zero to one less than the maximum number of ligands that may beattached to the metal. (X—Y) represents an ancillary ligand. Theseligands are referred to as “ancillary” because it is believed that theymay modify the photoactive properties of the molecule, as opposed todirectly contributing to the photoactive properties. The definitions ofphotoactive and ancillary are intended as non-limiting theories. Forexample, for Ir, n may be 0, 1 or 2 for bidentate ligands. Ancillaryligands for use in the emissive material may be selected from thoseknown in the art. Non-limiting examples of ancillary ligands may befound in PCT Application Publication WO 02/15645 A1 to Lamansky et al.at pages 89-90, which is incorporated herein by reference.

The metal forming the metal-carbene bond may be selected from a widerange of metals. Preferred metals include main group metals, 1^(st) rowtransition metals, 2^(nd) row transition metals, 3^(rd) row transitionmetals, and lanthanides. Although one skilled in the art typicallyexpects room temperature phosphorescence only from metal atoms thatexert a strong heavy atom effect, phosphorescent emission has beenobserved in Kunkley, et al. J. Organometallic Chem. 2003, 684, 113-116for a compound with a Nickel (Ni) metal, which is typically not expectedto exert a strong heavy atom effect. Thus, embodiments also includefirst row transition metal, such as Ni, and other metals that do notnormally exert a strong heavy atom effect but exhibits phosphorescentemission when coordinated to one or more carbene ligands. More preferredmetals include 3^(rd) row transition metals. The following are alsopreferred metals: Ir, Pt, Pd, Rh, Re, Ru, Os, Tl, Pb, Bi, In, Sn, Sb,Te, Au, and Ag. Most preferably, the metal is Iridium.

The most preferred embodiments are N-heterocyclic carbenes, whichBourissou has also reported as having “remarkable stability” as freecompounds in Bourissou et al. Chem Rev. 2000, 100, 39-91.

In one embodiment, the metal-carbene compound has the structure

and a ligand with the structure

in which R₄ is either an aromatic or an axnine group; and R₃ and R₄together form independently a 5 or 6-member cyclic group, which may becycloalkyl, cycloheteroalkyl, aryl or heteroaryl, and which mayoptionally be substituted by one or more substituents J.

In other embodiments, the metal-carbene compound may have one of thefollowing structures

in which the ligand has the corresponding structure selected from:

in which R₅ and R₆ may be alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′,N(R′)₂, SR′, C(O)R′, C(O)OR′, C(O)NR′₂, CN, CF₃, NO₂, SO₂, SOR′, SO₃R′,halo, aryl, and heteroaryl; and each R′ is independently selected fromH, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl;and additionally or alternatively, one or more of R₁ and R₂, R₂ and R₃,R₃ and R₅ and R₅ and R₆ together form independently a 5 or 6-membercyclic group, wherein said cyclic group is cycloalkyl, cycloheteroalkyl,aryl or heteroaryl; and wherein said cyclic group is optionallysubstituted by one or more substituents J.

In another embodiment the metal carbene compound has the structure:

and the carbene ligand has the structure

in which R₈, R₉, R₁₀, and R₁₁ may be alkyl, alkenyl, alkynyl, aralkyl,R′, O—R′, N(R′)₂, SR′, C(O)R′, C(O)OR′, C(O)NR′₂, CN, CF₃, NO₂, SO₂,SOR′, SO₃R′, aryl, and heteroaryl; each R′ is independently selectedfrom H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, andheteroaryl; and additionally or alternatively, one or more of R₁ and R₂,R₂ and R₈, R₈ and R₁₀, and R₆ and R₁₀ together form independently a 5 or6-member cyclic group, wherein said cyclic group is cycloalkyl,cycloheteroalkyl, aryl or heteroaryl; and wherein said cyclic group isoptionally substituted by one or more substituents J.

In another embodiment, the carbene-metal compound may have one of thestructures below:

in which the ligand has the structure selected from

in which each R₁₂ may be an alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′,N(R′)₂, SR′, C(O)R′, C(O)OR′, C(O)NR′₂, CN, CF₃, NO₂, SO₂, SOR′, SO₃R′,halo, aryl, and heteroaryl; each R′ is independently selected from H,alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; oralternatively, two R₁₂ groups on adjacent ring atoms may form a fused 5-or 6-membered cyclic group, wherein said cyclic group is cycloalkyl,cycloheteroalkyl, aryl or heteroaryl; and wherein said cyclic group isoptionally substituted by one or more substituents J; and d is 0, 1, 2,3 , or 4.

Another embodiment has a metal-carbene structure:

with a ligand having the structure

in which each R₁₃ may be an alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′,N(R′)₂, SR′, C(O)R′, C(O)OR′, C(O)NR′₂, CN, CF₃, NO₂, SO₂, SOR′, SO₃R′,halo, aryl, and heteroaryl; each R′ is independently selected from H,alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; oralternatively, two R₁₃ groups on adjacent ring atoms may form a fused 5-or 6-membered cyclic group, in which the cyclic group is cycloalkyl,cycloheteroalkyl, aryl or heteroaryl; and which is optionallysubstituted by one or more substituents J; and c may be 0, 1, 2, or 3.

Preferred embodiments include metal-carbene compounds having thestructure selected from:

with corresponding ligands having the structures selected from

in which Z² and Z₃ may be O, S, N—R₆, or P—R₆ and ring B isindependently an aromatic cyclic, heterocyclic, fused cyclic, or fusedheterocyclic ring with at least one carbon atom coordinated to metal M,in which ring B may be optionally substituted with one or moresubstituents R₁₄; and ring D is independently a cyclic, heterocyclic,fused cyclic, or fused heterocyclic ring with at least one carbon atomcoordinated to metal M, in which ring B may be optionally substitutedwith one or more substituents R¹⁵; and R¹⁴ and R¹⁵ are independentlyselected from alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)₂, SR′,C(O)R′, C(O)OR′, C(O)NR′₂, CN, CF₃, NO₂, SO₂, SOR′, SO₃R′, halo, aryl,and heteroaryl; each R′ is independently selected from H, alkyl,alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; oralternatively, two R¹⁴ groups on adjacent ring atoms and R¹⁵ groups onadjacent ring atoms form a fused 5- or 6-membered cyclic group, in whichthe cyclic group is cycloalkyl, cycloheteroalkyl, aryl or heteroaryl;and which is optionally substituted by one or more substituents J; b maybe 0, 1, 2, 3, or 4; and e may be 0, 1, 2, or 3.

In one embodiment the metal-carbene compound has the structure:

in which the ligand has the structure

Preferably, the compound has the structure:

and the ligand has the structure:

More preferably the metal-carbene has a structure selected from:

Another preferred embodiment has the structure:

in which the ligand has the structure

in which R₆ is an alkyl or aryl group. In a most preferred embodiment,the metal is Ir. Preferably, m is 3 and n is 0. In one embodiment, R₆ ismethyl. In another embodiment m is 2 and n is one. The ancillary ligandX—Y may be have one of the following structures:

Other preferred ancillary ligands are acetylacetonate, picolinate, andtheir derivatives.

Other preferred embodiments have the following general structures:

More preferred embodiments have the following structures:

and more preferred ligands have the following corresponding structures

Other embodiments may have the general structure:

and the ligand may have the corresponding structure

Preferably, the metal-carbene compound has the structure:

and the carbene ligand has the structure

Other preferred embodiments include:

in which the ligands have the structure:

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. It is understood thatvarious theories as to why the invention works are not intended to belimiting. For example, theories relating to charge transfer are notintended to be limiting.

MATERIAL DEFINITIONS

As used herein, abbreviations refer to materials as follows:

CBP: 4,4′-N,N-dicarbazole-biphenyl m-MTDATA4,4′,4″-tris(3-methylphenylphenly- amino)triphenylamine Alq₃:8-tris-hydroxyquinoline aluminum Bphen: 4,7-diphenyl-1,10-phenanthrolinen-BPhen: n-doped BPhen (doped with lithium) F₄-TCNQ:tetrafluoro-tetracyano-quinodimethane p-MTDATA: p-doped m-MTDATA (dopedwith F₄-TCNQ) Ir(ppy)₃: tris(2-phenylpyridine)-iridium Ir(ppz)₃:tris(1-phenylpyrazoloto,N,C(2′)iridi- um(III) BCP:2,9-dimethyl-4,7-diphenyl-1,10- phenanthroline TAZ:3-phenyl-4-(1′-naphthyl)-5-phenyl- 1,2,4-triazole CuPc: copperphthalocyanine. ITO: indium tin oxide NPD:N,N′-diphenyl-N-N′-di(1-naphthyl)- benzidine TPD:N,N′-diphenyl-N-N′-di(3-toly)-benzidine BAlq:aluminum(III)bis(2-methyl-8-hydroxy- quinolinato)4-phenylphenolate mCP:1,3-N,N-dicarbazole-benzene DCM: 4-(dicyanoethylene)-6-(4-dimethyl-aminostyryl-2-methyl)-4H-pyran DMQA: N,N′-dimethylquinacridonePEDOT:PSS: an aqueous dispersion of poly(3,4- ethylenedioxythiophene)with polystyrenesulfonate (PSS) 1-Ph-3-Me-imid1-phenyl-3-methyl-imidazolin-2- ylidene-C,C^(2′) 1-Ph-3-Me-benzimidfac-iridium(III)tris(1-phenyl-3-methyl-benzimidazolin-2-ylidene-C,C^(2′)) mer-(F₂ppz)₂Ir(1-Ph-3-Me-imid)mer-iridium(III)bis[(2-(4′,6′-difluoro-phenyl)-2-pyrazolinato-N,C^(2′))](1-phenyl-3-methyl-imidazolin-2-ylidene- C,C^(2′))mer-(2-(tpy)₂Ir(1-Ph-3-Me-imid) mer-iridium(III)bis[(2-(4′-methylphenyl)-2-pyridinato-N,C²)](1-phenyl-3-methyl-imidazolin-2-ylidene- C,C²fac-(2-(tpy)₂Ir(1-Ph-3-Me-imid)fac-iridium(III)bis[(2-(4′-methylphenyl)-2-pyridinato-N,C^(2′))](1-phenyl-3-methyl-imidazolin-2-ylidene-C,C^(2′)) [(1-Ph-3-Me-imid)₂IrCl]₂Iridium(III)bis(1-phenyl-3-methyl- imidazolin-2-ylidene-C,C^(2′))chloride (1-Ph-3-Me-imid)₂Ir(t-Bu-bpy)⁺Iridium(III)bis[(1-phenyl-3-methyl-imidazolin-2-ylidene-C,C^(2′))](4,4′-di-tert- butyl-(2,2′)bipyridinyl)mer-Ir(1-Ph-3-Me-imid)₃ mer-iridium(III)tris(1-phenyl-3-methyl-imidazolin-2-ylidene-CC^(2′)) (Ir-Fl-Me-imid)₃tris(1-(2^(′)-(9′,9′-dimethyl)fluorenyl)-3-methyl-imidazolin-2-ylidene-C,C3′) iridium(III)

EXPERIMENTAL

Specific representative embodiments of the invention will now bedescribed, including how such embodiments may be made. It is understoodthat the specific methods, materials, conditions, process parameters,apparatus and the like do not necessarily limit the scope of theinvention.

Synthesis of Imidazolate Carbene Precursors

1-Phenylimidazole was purchased from Aldrich. All other aryl imidazoleswere prepared by a modified Ullmann coupling reaction between imidazoleor benzimidazole and the appropriate aryl iodide in anhydrousN,N-dimethylformamide using a CuI/1,10-phenanthroline catalyst andCs₂CO₃ base, as described in Klapars, et al, J. Am. Chem. Soc., 2001,123; 7727-7729. The carbene precursor imidazolates were prepared bymethylating the corresponding imidazoles with excess methyl iodide intoluene.

Example 1 Synthesis of 1-phenyl-3-methylimidazolate iodide

1-phenyl-3-methylimidazolate iodide was synthesized using the modifiedUllmann coupling reaction described above. ¹H NMR (250MHz, CDCl₃), ppm:10.28 (s, 1H), 7.77-7.70 (m, 4H), 7.56-7.46 (m, 3H), 4.21 (s, 3H).

Example 2 Synthesis of 1-Phenyl-3-methyl-benzimidazolate iodide

In the dark, an oven-dried 50 ml round-bottomed flask containing a stirbar was charged with CuI (0.171 g, 0.1 eq.), benzimidazole (1.273 g, 1.2eq.), and cesium carbonate (6.138 g, 2.1 eq.) respectively. Theround-bottomed flask with the contents was sealed with septa anddegassed with argon for 15 minutes. Iodobenzene (1 ml, 1 eq.),1,10-Phenanthroline (0.323 g, 0.2 eq.), and dimethylformamide (25 ml)were then successively added into the round-bottomed flask under acontinuous flow of argon. The reaction mixture was degassed with argonfor 30 minutes. The reaction was stirred with heating via an oil bath at110° C. for 24 hours in the dark under nitrogen. The reaction mixturewas cooled to ambient temperature and concentrated in vacuo. 10 ml ofethyl acetate was added into the concentrated reaction mixture. It wasthen filtered and washed with 30 ml of ethyl acetate. The filtrate wasconcentrated under vacuo to give the crude product. The crude productwas purified by column chromatography on silica gel (40% ethyl acetate:60% hexane as the eluent) providing 0.780 g of 1-Phenyl benzoimidazole(45% yield) as yellow liquid.

Methyl iodide (0.550 ml, 2.2 eq.) was syringed into a 25 mlround-bottomed flask charged with 1-phenyl benzoimidazole (0.780 g, 1eq.) and toluene (15 ml). The reaction was stirred and heated at 30° C.for 24 hours. The white precipitate was filtered and washed with 20 mlof toluene. The white precipitate was air-dried and weighed to give0.725 g of 1-phenyl-3-methyl-benzimidizolate iodide (54% yield).

Synthesis of Iridium Imidazole Carbene Complexes

Example 3 Synthesis of mer-iridium(III)bis[(2-(4′,6′-difluorophenyl)-2-pyrazolinato-N,C^(2′))](1-phenyl-3-methyl-imidazolin-2-ylidene-C,C^(2′))

A 25 ml round-bottomed flask was charged with 0.014 g of silver(I)oxide, 0.030 g of 1-phenyl-3-methyl-imidazolate iodide, 0.062 g of[(F2ppz)₂IrCl]₂, and 15 ml of 1,2-dichloroethane. The reaction wasstirred and heated with an oil bath at 77° C. for 15 hours in the darkunder nitrogen while protected from light with aluminum foil. Thereaction mixture was cooled to ambient temperature and concentratedunder reduced pressure. Filtration through Celite using dichloromethaneas the eluent was performed to remove the silver(I) salts. A lightyellow solution was obtained and addition of methanol gave 0.025 g (30%yield) of iridium complex as a colorless solid.

¹H NMR (500MHz, CDCl₃), ppm: 8.24 (d, 1H, J=2.8 Hz), 8.16 (d, 1H, J=2.8Hz), 7.43 (d, 1H, J=1.9 Hz), 7.15 (d, 1H, J=7.5 Hz), 6.96 (ddd, 1H,J=7.5, 7.0, 1.9 Hz), 6.93 (dd, 1H, J=7.0, 1.9 Hz), 6.82 (m, 2H), 6.78(d, 1H, J=1.9 Hz), 6.47 (ddd, 1H, J=11.7, 8.4, 2.3 Hz), 6.43 (ddd, 1H,J=11.7, 8.4, 2.3 Hz), 6.29 (t, 1H, J=2.3 Hz), 6.28 (t, 1H, J=2.3 Hz),6.14 (dd, 1H, J=7.5, 2.3 Hz), 5.85 (dd, 1H, J=8.0, 2.3 Hz), 3.29 (s,3H).

FIG. 3 shows the ¹H NMR spectra of mer-(F₂ppz)₂Ir(1-Ph-3-Me-imid) inCDCl₃.

Example 4 Synthesis of mer-iridium(III)bis[(2-(4′-methylphenyl)-2-pyridinato-N,C^(2′))](1-phenyl-3-methyl-imidazolin-2-ylidene-C,C^(2′))

A 50 ml round-bottomed flask was charged with 0.103 g of silver(I)oxide, 0.118 g of 1-phenyl-3-methyl-imidazolate iodide, 0.168 g of[(tpy)₂IrCl]₂, and 25 ml of 1,2-dichloroethane. The reaction was stirredand heated with an oil bath at 77° C. for 15 hours in the dark undernitrogen while protected from light with aluminum foil. The reactionmixture was cooled to ambient temperature and concentrated under reducedpressure. Filtration through Celite using dichloromethane as the eluentwas performed to remove the silver(I) salts. A yellow solution wasobtained and further purified by flash column chromatography on silicagel using dichloromethane as the eluent that was reduced in volume toca. 2 ml. Addition of methanol gave 0.121 g (59% yield) of iridiumcomplex as a bright yellow solid.

FIG. 4 shows the ¹H NMR spectra of mer-(tpy)₂Ir(1-Ph-3-Me-imid) inCDCl₃. FIG. 6 shows the plot of current (μA) vs. voltage (V) of amer-(tpy)₂Ir(1-Ph-3-Me-imid) compound with ferrocene as an internalreference. A solvent of DMF with 0.1M Bu₄N⁺PF₆ ⁻ is used. FIG. 9 showsthe emission spectra of mer-(tpy)₂Ir(1-Ph-3-Me-imid) in 2-MeTHF at roomtemperature and at 77K. The compound exhibits lifetimes of 1.7 μs atroom temperature and 3.3 μs at 77K.

Example 5 Synthesis of fac-iridium(III)bis[(2-(4′-methylphenyl)-2-pyridinato-N,C^(2′))](1-phenyl-3-methyl-imidazolin-2-ylidene-C,C^(2′))

A 200 ml quartz flask was charged with 0.0.059 g ofmer-(tpy)₂Ir(1-Ph-3-Me-imid) and 50 ml of acetonitrile and sparged withnitrogen for five minutes. The mixture was photolyzed for 63 hours using254 nm light. After photolysis the solvent was removed under reducedpressure and the yellow solid was taken up in 2 ml dichloromethane.Addition of methanol gave 0.045 g (75% yield) of iridium complex as abright yellow solid that was collected by centrifuge.

FIG. 5 shows the ¹H NMR spectra of fac-(tpy)₂Ir(1-Ph-3-Me-imid) inCDCl₃. FIG. 7 shows the plot of current (μA) vs. voltage (V) of afac-(tpy)₂Ir(1-Ph-3-Me-imid) compound with ferrocene as an internalreference. A solvent of DMF with 0.1M Bu₄N⁺PF₆ ⁻ is used. FIG. 8 showsthe absorption spectra of fac-(tpy)₂Ir(1-Ph-3-Me-imid) andmer-(tpy)₂Ir(1-Ph-3-Me-imid) in CH₂Cl₂. FIG. 10 shows the emissionspectra of fac-(tpy)₂Ir(1-Ph-3-Me-imid) in 2-MeTHF at room temperatureand at 77K. The compound exhibits lifetimes of 1.7 μs at roomtemperature and 3.3 μs at 77K.

Example 6 Synthesis of Iridium(III)bis(1-phenyl-3-methyl-imidazolin-2-ylidene-C,C^(2′)) chloride dimer

A 100 ml round-bottomed flask was charged with 0.428 g of silver(I)oxide, 0.946 g of 1-phenyl-3-methyl-imidazolate iodide, 0.301 g ofiridium trichloride hydrate, and 60 ml of 2-ethoxyethanol. The reactionwas stirred and heated with an oil bath at 120° C. for 15 hours undernitrogen while protected from light with aluminum foil. The reactionmixture was cooled to ambient temperature and the solvent was removedunder reduced pressure. The black mixture was extracted with ca. 20 mldichloromethane and the extract was reduced to ca. 2 ml volume. Additionof methanol gave 0.0160 g (30% yield) of the iridium dimer complex as anoff-white solid.

FIG. 11 shows the ¹H NMR spectra of [(1-Ph-3-Me-imid)₂IrCl]₂ in CDCl₃.

Example 7 Synthesis of mer-iridium(III)tris(1-phenyl-3-methyl-imidazolin-2-ylidene-C,C^(2′))

A 50 ml round-bottomed flask was charged with 0.076 g of silver(I)oxide, 0.109 g of 1-phenyl-3-methyl-imidazolate iodide, 0.029 g ofiridium trichloride hydrate, and 20 ml of 2-ethoxyethanol. The reactionwas stirred and heated with an oil bath at 120° C. for 15 hours undernitrogen while protected from light with aluminum foil. The reactionmixture was cooled to ambient temperature and concentrated under reducedpressure. Filtration through Celite using dichloromethane as the eluentwas performed to remove the silver(I) salts. A white solid was obtainedafter removing the solvent in vacuo and was washed with methanol to give0.016 g (24% yield) of meridional tris-iridium complex as a white solid.

FIG. 15 shows the ¹H NMR spectra of mer-Ir(1-Ph-3-Me-imid)₃ in CDCl₃.FIG. 16 shows the ¹³C NMR spectra of mer-Ir(1-Ph-3-Me-imid)₃ in CDCl₃.FIG. 17 shows the plot of current (μA) vs. voltage (V) of amer-Ir(1-Ph-3-Me-imid)₃ compound with ferrocene as an internalreference. A solvent of DMF with 0.1M Bu₄N⁺PF₆ ⁻ is used. FIG. 18 showsthe emission spectra of mer-Ir(1-Ph-3-Me-imid)₃ in 2-MeTHF at roomtemperature and at 77K.

Example 8 Synthesis of fac-iridium(III)tris(1-phenyl-3-methyl-imidazolin-2-ylidene-C,C2′)

A 50 ml round-bottomed flask was charged with 0.278 g of silver(I)oxide, 0.080 g of 1-phenyl-3-methyl-imidazolate iodide, 0.108 g of[(1-Ph-3-Me-imid)2IrCl]2, and 25 ml of 1,2-dichloroethane. The reactionwas stirred and heated with an oil bath at 77° C. for 15 hours undernitrogen while protected from light with aluminum foil. The reactionmixture was cooled to ambient temperature and concentrated under reducedpressure. Filtration through Celite using dichloromethane as the eluentwas performed to remove the silver(I) salts. A light brown solution wasobtained and further purified by flash column chromatography on silicagel using dichloromethane as the eluent and was then reduced in volumeto ca. 2 ml. Addition of methanol gave 0.010 g (8% yield) of iridiumcomplex as a colorless solid.

FIG. 19 shows the ¹H NMR spectra of fac-Ir(1-Ph-3-Me-imid)₃ in CDCl₃.FIG. 20 shows the absorption spectra of fac-Ir(1-Ph-3-Me-imid)₃ inCH₂Cl₂. FIG. 21 shows the emission spectra of fac-Ir(1-Ph-3-Me-imid)₃ in2-MeTHF at room temperature and at 77K. The compound exhibits lifetimesof 0.50 μs at room temperature and 6.8 μs at 77K.

Example 9 Synthesis of fac-iridium(III)tris(1-phenyl-3-methyl-benzimidazolin-2-ylidene-C,C^(2′))

A 25 ml round-bottomed flask was charged with 0.165 g of silver(I)oxide, 0.200 g of 1-phenyl-3-methyl-benzimidazolate iodide, 0.0592 g ofiridium trichloride hydrate, and 15 ml of 2-ethoxyethanol. The reactionwas stirred and heated with an oil bath at 120° C. for 24 hours undernitrogen while protected from light with aluminum foil. The reactionmixture was cooled to ambient temperature and concentrated under reducedpressure. Flash column chromatography on Celite using dichloromethane asthe eluent was performed to remove the silver(I) salts. A brown oil wasobtained and further purified by flash column chromatography on silicagel using dichloromethane as the eluent to give 0.050 g of facialtris-iridium complex (33% yield) as an off-white solid.

FIG. 22 shows the ¹H NMR spectra of 1-Ph-3-Me-benzimid in CDCl₃. FIG. 23shows the ¹H NMR spectra of fac-Ir(1-Ph-3-Me-benzimid)₃ in CDCl₃. FIG.24 shows the plot of current (mA) vs. voltage (V) of afac-Ir(1-Ph-3-Me-benzimid)₃ compound with ferrocene as an internalreference. A solvent of anhydrous DMF is used. FIG. 25 shows theemission spectra of fac-Ir(1-Ph-3-Me-benzimid)₃ in 2-MeTHF at roomtemperature and at 77K. The compound emits a spectrum at CIE 0.17, 0.04.The lifetime measurements of an Ir(1-Ph-3-Me-benzimid)₃ compound isshown on Table I.

TABLE I Temperature Peak wavelength Lifetime, t Room temperature 402 nm0.32 μs Room temperature 420 nm 0.29 μs 77 K 400 nm 2.6 μs 77 K 420 nm2.7 μs

Example 9 Synthesis of iridium(III)bis(1-phenyl-3-methyl-imidazolin-2-ylidene-C,C2′)(4,4′-di-tert-butylbipyidyl)hexafluorophosphate

A 25 ml round-bottomed flask was charged with 0.010 g of[(1-Ph-3-Me-imid)2IrCl]2, 0.005 g of 4′4′-di-tert-butyl-bipyridine and15 ml of dichloromethane. The reaction was stirred at room temperaturefor 16 hours. The solvent was removed under reduced pressure and theresultant yellow solid was dissolved in ca. 2 ml methanol. Addition ofan aqueous ammonium hexafluorophosphate solution produced a yellowprecipitate. The precipitate was collected by filtration, washed withwater and dried. Chromatography on silica addition of hexanes gave 0.015g (82% yield) of iridium complex as an orange solid.

FIG. 12 shows the ¹H NMR spectra of (1-Ph-3-Me-imid)₂Ir(t-Bu-bpy)⁺ inCDCl₃. FIG. 13 shows the absorption spectra of(1-Ph-3-Me-imid)₂Ir(t-Bu-bpy)⁺ in CH₂Cl₂. FIG. 14 shows the emissionspectra of (1-Ph-3-Me-imid)₂Ir(t-Bu-bpy)⁺ in 2-MeTHF at 77K and(1-Ph-3-Me-imid)₂Ir(t-Bu-bpy)⁺ in CH₂Cl₂ at room temperature. Thecompound exhibits lifetimes of 0.70 μs at room temperature and 6.0 μs at77K.

While the present invention is described with respect to particularexamples and preferred embodiments, it is understood that the presentinvention is not limited to these examples and embodiments. The presentinvention as claimed therefore includes variations from the particularexamples and preferred embodiments described herein, as will be apparentto one of skill in the art.

1. A compound selected from the group consisting of:

wherein Z³ is selected from the group consisting of O, S, N—R₆, or P—R₆,wherein R₆ is independently selected from the group consisting of alkyl,alkenyl, alkynyl, aralkyl, O—R′, N(R′)₂, SR′, C(O)R′, C(O)OR′, C(O)NR′₂,CN, CF₃, NO₂, SO₂, SOR′, SO₃R′, halo, and heteroaryl; each R′ isindependently selected from H, alkyl, alkenyl, alkynyl, heteroalkyl,aralkyl, aryl, and heteroaryl; and A is independently selected from C,N, O, P, or S; (X—Y) is a bidentate photoactive ligand or a bidentateancillary ligand; ring B is independently an aromatic cyclic,heterocyclic, fused cyclic, or fused heterocyclic ring, wherein ring Bcan be optionally substituted with one or more substituents R¹⁴; andring D is independently a cyclic, heterocyclic, fused cyclic, or fusedheterocyclic ring with at least one carbon atom coordinated to metal M,wherein ring D can be optionally substituted with one or moresubstituents R¹⁵; and R¹⁴ and R¹⁵ are independently selected from alkyl,alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)₂, SR′, C(O)R′, C(O)OR′,C(O)NR′₂, CN, CF₃, NO₂, SO₂, SOR′, SO₃R′, halo, aryl, and heteroaryl;each R′ is independently selected from H, alkyl, alkenyl, alkynyl,heteroalkyl, aralkyl, aryl, and heteroaryl; or alternatively, two R¹⁴groups on adjacent ring atoms and R¹⁵ groups on adjacent ring atoms forma fused 5- or 6-membered cyclic group, wherein said cyclic group iscycloalkyl, cycloheteroalkyl, aryl or heteroaryl; and wherein saidcyclic group is optionally substituted by one or more substituents J; bis 0, 1, 2, 3, or 4; e is 0, 1, 2, or 3; m has a value from 1 to themaximum number of ligands that may be attached to the metal; and m+n isthe maximum number of ligands that may be attached to metal M.
 2. Thecompound of claim 1, wherein the compound is selected from the groupconsisting of:


3. The compound of claim 2, wherein the compound has the structure:


4. The compound of claim 2, wherein the compound has the structure:

R₈ and R₁₀ are independently selected from the group consisting of H,alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)₂, SR′, C(O)R′,C(O)OR′, C(O)NR′₂, CN, CF₃, NO₂, SO₂, SOR′, SO₃R′, halo, aryl, andheteroaryl; each R′ is independently selected from H, alkyl, alkenyl,alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; and additionally oralternatively, R₈ and R₁₀ together form a 5 or 6-member cyclic group,wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl, orheteroaryl; and wherein said cyclic group is optionally substituted byone or more substituents J.
 5. The compound of claim 4, wherein thecompound is selected from the group consisting of:


6. The compound of claim 5, wherein the compound has the structure:

wherein R₆ is an alkyl.
 7. The compound of claim 6, wherein M isselected from a group consisting of main group metals, 1^(st) rowtransition metals, 2^(nd) row transition metals, 3^(rd) row transitionmetals, and lanthanides.
 8. The compound of claim 7, wherein M isselected from the group consisting of Ir, Pt, Pd, Rh, Re, Ru, Os, Tl,Pb, Bi, In, Sn, Sb, Te, Au, and Ag.
 9. The compound of claim 8, whereinM is Ir.
 10. The compound of claim 9, wherein m is 3 and n is
 0. 11. Thecompound of claim 10, wherein R₆ is methyl.
 12. The compound of claim 9,wherein m is
 2. 13. The compound of claim 12, wherein X—Y is selectedfrom the group consisting of:

acetylacetonate, and picolinate.
 14. The compound of claim 5, whereinthe compound is selected from the group consisting of:


15. The compound of claim 14, wherein M is selected from a groupconsisting of main group metals, 1^(st) row transition metals, 2^(nd)row transition metals, 3^(rd) row transition metals, and lanthanides.16. The compound of claim 15, wherein M is selected from the groupconsisting of Ir, Pt, Pd, Rh, Re, Ru, Os, Tl, Pb, Bi, In, Sn, Sb, Te,Au, and Ag.
 17. The compound of claim 16, wherein M is Ir.
 18. Thecompound of claim 17, wherein m is 3 and n is
 0. 19. The compound ofclaim 17, wherein m is
 2. 20. The compound of claim 5, wherein thecompound has the structure

wherein R₆ is an alkyl group.
 21. The compound of claim 20, wherein M isselected from a group consisting of main group metals, 1^(st) rowtransition metals, 2^(nd) row transition metals, 3^(rd) row transitionmetals, and lanthanides.
 22. The compound of claim 21, wherein M isselected from the group consisting of Ir, Pt, Pd, Rh, Re, Ru, Os, Tl,Pb, Bi, In, Sn, Sb, Te, Au, and Ag.
 23. The compound of claim 22,wherein M is Ir.
 24. The compound of claim 23, wherein m is 3 and n is0.
 25. The compound of claim 24, wherein R₆ is methyl.
 26. The compoundof claim 23, wherein m is
 2. 27. The compound of claim 2, wherein thecompound is selected from the group consisting of:

wherein ring B is an aromatic cyclic, heterocyclic, fused cyclic, orfused heterocyclic ring with at least one carbon atom coordinated tometal M; and R₈ and R₁₀ are independently selected from the groupconsisting of H, alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)₂,SR′, C(O)R′, C(O)OR′, C(O)NR′₂, CN, CF₃, SO₂, SOR′, SO₃R′, halo, aryl,and heteroaryl; each R′ is independently selected from H, alkyl,alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; each R¹⁴is independently selected from alkyl, alkenyl, alkynyl, aralkyl, R′,O—R′, N(R′)₂, SR′, C(O)R′, C(O)OR′, C(O)NR′₂, CN, CF₃, NO₂, SO₂, SOR′,or SO₃R′ halo, aryl, and heteroaryl; each R′ is independently selectedfrom H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl, andheteroaryl; or alternatively, two R¹⁴ groups on adjacent ring atoms forma fused 5- or 6-membered cyclic group, wherein said cyclic group iscycloalkyl, cycloheteroalkyl, aryl or heteroaryl; and wherein saidcyclic group is optionally substituted by one or more substituents J; bis 0, 1, 2, 3, or
 4. 28. The compound of claim 2, wherein the compoundis selected from the group consisting of:

wherein R₈ and R₁₀ are independently selected from the group consistingof H, alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)₂, SR′, C(O)R′,C(O)OR′, C(O)NR′₂, CN, CF₃, NO₂, SO₂, SOR′, SO₃R′, halo, aryl, andheteroaryl: each R′ is independently selected from H, alkyl, alkenyl,alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl.
 29. The compound ofclaim 1, wherein the compound is selected from the group consisting of:

wherein R₈ and R₁₀ are independently selected from the group consistingof H, alkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)₂, SR′, C(O)R′,C(O)R′, C(O)NR′₂, CN, CF₃, NO₂, SO₂, SOR′, SO₃R′, halo, aryl, andheteroaryl; each R′ is independently selected from H, alkyl, alkenyl,alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; and additionally oralternatively, R₈ and R₁₀ together form a 5 or 6-member cyclic group,wherein said cyclic group is cycloalkyl, cycloheteroalkyl, aryl, orheteroaryl; and wherein said cyclic group is optionally substituted byone or more substituents J: each R₁₂ is independently selected fromalkyl, alkenyl, alkynyl, aralkyl, R′, O—R′, N(R′)₂, SR′, C(O)R′,C(O)OR′, C(O)NR′₂, CN, CF₃, NO₂, SO₂, SOR′, SO₃R′, halo, aryl, andheteroaryl; each R′ is independently selected from H, alkyl, alkenyl,alkynyl, heteroalkyl, aralkyl, aryl, and heteroaryl; or alternatively,two R₁₂ groups on adjacent ring atoms form a fused 5- or 6-memberedcyclic group, wherein said cyclic group is cycloalkyl, cycloheteroalkyl,aryl or heteroaryl; and wherein said cyclic group is optionallysubstituted by one or more substituents J; and d is 0, 1, 2, 3, or 4.30. The compound of claim 1, wherein the compound is selected from thegroup consisting of:

wherein each R₁₂ is independently selected from alkyl, alkenyl, alkynyl,aralkyl, R′, O—R′, N(R′)₂, SR′, C(O)R′, C(O)OR′, C(O)NR′₂, CN, CF₃, NO₂,SO₂, SOR′, SO₃R′, halo, aryl, and heteroaryl; each R′ is independentlyselected from H, alkyl, alkenyl, alkynyl, heteroalkyl, aralkyl, aryl,and heteroaryl; or alternatively, two R₁₂ groups on adjacent ring atomsform a fused 5- or 6-membered cyclic group, wherein said cyclic group iscycloalkyl, cycloheteroalkyl, aryl or heteroaryl; and wherein saidcyclic group is optionally substituted by one or more substituents J;and d is 0, 1, 2, 3, or
 4. 31. The compound of claim 1, wherein M isselected from a group consisting of main group metals, 1^(st) rowtransition metals, 2^(nd) row transition metals, 3^(rd) row transitionmetals, and lanthanides.
 32. The compound of claim 31, wherein M isselected from the group consisting of Ir, Pt, Pd, Rh, Re, Ru, Os, Tl,Pb, Bi, In, Sn, Sb, Te, Au, and Ag.
 33. The compound of claim 32,wherein n is zero and m is the maximum number of ligands that may beattached to metal M.
 34. The compound of claim 33, wherein M is Ir.